tests, there is no significant difference in the sectional efficiency except at extreme loads. This was
confirmed by the composition profiles presented in
Figure 15.
Tray Pressure Drop
Figures 16-21 show the measured tray pressure drop results for the iC4/nC4 system at 100 and 165 psia
(6.9 and 11.4 bar). Also included are the pressure drop results of the type 2 valve tray and the sieve tray
tested in 1987. As shown in
Figures 16 and 19 the pressure drops of the MVGT tray are significantly
lower than those of the type 2 valve tray for the iC4/nC4 system at both 100 and 165 psia (6.9 and 11.4
bar) pressures. Compared to the 1987 sieve tray with the iC4/nC4 system at 165 psia, the MVGT tray has
similar tray pressure drop at lower to medium vapor rates, but a lower pressure drop at high vapor rates as
shown in
Figures 18 and 19. Figures 20 and 21 show the comparison of the pressure drops of the top
four trays and the bottom four trays for 100 and 165 psia (6.9 and 11.4 bar) column pressures. As
indicated from those two figures, there is no significant difference in the sectional pressure drop observed
except at flood conditions. At flood, the top section (trays 5 to 8) has a higher pressure drop than the
bottom section (trays 1 to 4), indicating the flood is initiated from the top of the column.
Gamma Scan Results
Gamma ray scanning was used to measure the process density and calculate the liquid volume fractions at
various locations inside the column.
Figure 22 compares the liquid volume fraction at the centerline for
the MVGT tray to that for the type 2 valve tray. Above the tray floor the liquid volume fraction declines
more rapidly with elevation for the MVGT tray than the Type 2 valve tray. This indicates that at the same
Cs, (capacity factor based on cross-sectional area), less material is entrained above the MVGT tray. This
is true for the iC4/nC4 system at 100 psia (6.9 bar) as well.
The liquid volume fraction profiles were integrated to obtain the liquid holdup on Tray 4. As shown in
Figure 23 the tray holdup of the MVGT tray is generally lower than that of the type 2 valve tray.
The profile of the downcomer liquid volume fraction for the MVGT tray is compared to the type 2 valve
tray in
Figure 24. For the 165 psia (11.4 bar) iC4/nC4 system the profiles for the two trays are quite
similar. As shown in this figure, a discontinuity of liquid volume fraction occurred for the MVGT tray
around the downcomer bottom plate that is located at 9 in (229 mm) elevation, 5 inch (127 mm) above the
tray deck.
The liquid volume fraction profiles in the downcomer were integrated to obtain the overall downcomer
backup. Since the MVGT tray has a truncated downcomer with a bottom plate 5 in. (127 mm) above the
tray deck, the integration starts from the bottom plate where the bubbler was installed.
Figure 25
compares the backup measured by the gamma ray to the bubbler measurements for the tray 5 downcomer
and gamma ray results for the type 2 valve tray. It can be seen for the iC4/nC4 system at 165 psia (11.4
bar), the downcomer backup of the MVGT tray is less than that of the type 2 valve tray. As indicated
from this figure, the backups measured by the gamma ray are in agreement with those measured by the
bubblers except at flood conditions. Similar results were obtained from the iC4/nC4 system at 100 psia
(6.9 bar).
Since a complete listing of all gamma ray data is quite large, these results are available on request.
Representative data from the gamma ray scans are given in
Table 6. The tray 4 liquid holdup and tray 5
downcomer backup are given in the main data tables,
Tables 2 to 4.
